Electrophotographic recording material having a layered structure of charge generating and charge transport layers

ABSTRACT

This invention relates to an electrophotographic recording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer in which the dyestuff corresponds to the following general formula   wherein: A stands for nitrogen or CR, with R being hydrogen, alkyl with 1 to 4 carbon atoms, phenyl, which may be substituted by alkyl with 1 to 4 carbon atoms, or halogen, and B and B&#39;&#39; may be the same or different and stand for an aromatic or heterocyclic group, which may be substituted and D stands for CH- or N-, and of a transparent top layer of insulating materials containing at least one charge transporting compound.

United States Patent Wiedemann et al.

[ ELECTROPHOTOGRAPHIC RECORDING MATERIAL HAVING A LAYERED STRUCTURE OF CHARGE GENERATING AND CHARGE TRANSPORT LAYERS [75] Inventors: Wolfgang Wiedemann,

Geisenheim-Johannisberg; Horst Zimmer, Niedernhausen, Taunus, both of Germany [73] Assignee: Hoechst Aktiengesellschaft, Germany 22 1 Filed: Apr. 25, 1973 211 Appl. No.: 354,202

OTHER PUBLICATIONS Abstracts of Belgium, 763540, A89 E|4G8, Al2L2.

Primary Examiner-Norman G. Torchin Assistant Examiner.l0hn L. Goodrow Attorney, Agent, or Firm-James E. Bryan 5] July 22, 1975 [5 7] ABSTRACT This invention relates to an electrophotographic recording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque. charge carrier producing dyestuff layer in which the dyestuff corresponds to the following general formula A B A f NH NH j D D A B' A wherein:

A stands for nitrogen or CR, with R being hydrogen, alkyl with l to 4 carbon atoms, phenyl, which may be substituted by alkyl with l to 4 carbon atoms, or halogen, and

B and B may be the same or different and stand for an aromatic or heterocyclic group, which may be substituted and D stands for =CH- or =N-,

and of a transparent top layer of insulating materials containing at least one charge transporting compound,

14 Claims, 3 Drawing Figures PATENTEDJIJL22 3.895944 SHEET 1 PATENTEDJULZ'Z 1915 11895944 sum 2 Fig. 3

400 soo 600 700 1 nm PATENTEDJUL22 ms SHEET FORMULAE- B J B. Al'Yl- Heterocyclus ELECTROPI-IOTOGRAPI-IIC RECORDING MATERIAL HAVING A LAYERED STRUCTURE OF CHARGE GENERATING AND CHARGE TRANSPORT LAYERS This invention relates to an electrophotographic recording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer in which the dyestuff corresponds to the following general A stands for nitrogen or CR, with R being hydrogen, alkyl with l to 4 carbon atoms, phenyl, which may be substituted by alkyl with l to 4 carbon atoms, or halogen, and

B and B may be the same or different and stand for an aromatic or heterocyclic group, which may be substituted and D stands for =CH- or =N, and of a transparent top layer of insulating materials containing at least one charge transporting compound.

It is known from German Offenlegungsschriften Nos. l,597,877 and 1,797,342 for electrophotographic re cording material to extend the spectral sensitivity of selenium layers to the red spectral range by a double layer arrangement, e.g. with phthalocyanine dispersion layers. Disadvantageous are the vacuum vapor depositions of selenium requiring high technical expenditure, the brittleness of comparatively thick selenium layers, the poor adhesion of adjacent heterogeneous constituents in these layers and the only difficulty realizable uniformly wetting coating with the corresponding dispersions. Furthermore, no optimum light-sensitivities can be achieved as a result of the absorption behavior and the different charge conducting mechanisms of selenium and phthalocyanine in the double layer arrangement.

From U.S. Pat. No. 3,573,906, for example, there are also known photoconductive double layers containing an organic, possibly photoconductive, insulating layer between the support material and the vapor-deposited selenium layer in order to impart adhesion. Such a layer construction, howoever, considerably hinders the necessary charge transport so that, in this case, too, no higher light-sensitivities are obtainable.

Furthermore, from German Auslegeschrift No. l,964,8 l7, it is known to provide vapor-deposited selenium layers with a layer of an organic, photoconductive insulating material which is substantially insensitive to light in the visible range of the spectrum. According to German Offenlegungsschrift No. 2,l20,9l2, it has also been suggested to use those light-sensitive layer arrangements for electrophotographic recording materi' als which contain, as the charge carrier producing layer, an inorganic material, such as the sulfide, selehide, sulfoselenide or telluride of cadmium or zinc, and, as the charge carrier transporting layer, an organic material with at least 20 per cent by weight of 2,4,7-trinitro-9-fluorenone. A disadvantage of the production of these layers with inorganic photoconductors is the exact observation of the vapor deposition conditions of selenium or the exact adjustment of the mixtures in order to obtain a good photoconductive modification of the inorganic materials. Furthermore, the adhesion of selenium to conductive support material, such as to aluminum, is insufficient. Fatigue in repeated charge/exposure cycles does not allow the use in electrophotographic copying devices.

Japanese Patent application No. 43-26710 already discloses photoconductive double layers of organic materials on a conductive support. According to that application, a lower, relatively thick layer of a considerably diluted homogeneous solution of a sensitizer in a binder is provided with an upper transparent lightsensitive layer. This layer construction, however, only offers a relatively low sensitivity increase only little meeting technical demands. Another known suggestion according to German Offenlegungsschrift No. 1,909,742 is to repeatedly pour a sensitizer solution over a photoconductive layer and to evaporate the solvent. A disadvantage thereof is the low mechanical resistance of the applied layer as a result of insufficient cohesion and adhesion of the applied sensitizer. Furthermore, repeated coating is cumbersome.

The construction of photoconductive double layers containing a dyestuff layer is also known, e.g. from Belgian Patent Nos. 763,389 and 763,541, but for this layer construction, top layers are used which allow no sensitivities satisfying highest demands and, as regards adhesion between the dyestuff layer and the top layer, do not represent an optimization and are not sufficiently resistant to mechanical attack, e.g. in electrophotographic copying devices, particularly to that due to the cleaning of the photoconductive layer.

It is the object of the present invention to provide an organic photoconductor layer highly light-sensitive for the xerographic copying procedure which overcomes the described disadvantages and the adhesion of which between the various layers satisfies the highest technical demands, which exhibits substantially no wear or fatigue and which, even after repeated used, may be used again rapidly.

The present invention provides an electrophotographic recording material consisting of an electroconductive support material with a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer in which the dyestuff corresponds to the following general formula wherein:

A stands for nitrogen or CR, with R being hydrogen, alkyl with l to 4 carbon atoms, phenyl, which may be suubstituted by alkyl with l to 4 carbon atoms, or halogen, and

B and B may be the same or different and stand for an aromatic or heterocyclic group, which may be substituted and D stands for =CH- or =N, and of a transparent top layer of insulating materials containing at least one charge transporting compound, which is characterized in that the transparent top layer consists of a mixture of a binder with a charge trans porting, monomer. heterocyclic compound substituted by at least one dialkyl amino group or two alkoxy groups and having an extended rr-electron system or with a condensation product of 3-bromo-pyrene and formaldehyde.

By means of the invention, it is possible to obtain highly light-sensitive, photoconductive double layers for the electrophotographic recording material of the invention which have a high mechanical resistance and may be arranged on a cylindrical drum, for example, or may circulate as an endless belt without exhibiting special signs of wear and thus are very suitable for the use 20 in electrophotographic copying devices. The high lightsensitivity particularly results from the fact that the charge transporting compound present in the transparent top layer is sensitized by the charge carrier produc ing dyestuff layer in that the charge carriers, i.e. electronsvor defect electrons, are taken up by the top layer.

In a preferred embodiment, the organic dyestuff layer has a thickness in the range from about 0.005 to about 2 uum. High concentration of excited dyestuff molecules is achieved thereby in the dyestuff layer and at the boundary surface between the dyestuff layer and the top layer. Furthermore, the adhesion between the electroconductive support material and the top layer is not impaired.

In a preferred embodiment, the transparent top layer has a thickness in the range from about to about purn. This assures a sufficiently high charge.

The invention will be further illustrated by reference to the accompaning drawing in which:

FIG. 1 shows an electrophotographic material according to the invention,

FIG. 2 shows an electrophotographic material according to the invention on a metallized plastic support,

FIG. 3 is a graph showing the spectral light-sensitivity of one of the double layers of the present invention, and

Formulae 14 are examples of dyestuff suitable for use in the present invention.

FIG. 1 shows a material consisting of an electroconductive support 1, an organic dyestuff layer 2, and an organic transparent top layer 3.

in FIG. 2 the support is a metallized plastic layer 1, 4, which carries, under thhe photoconductive double layer composed of an organic dyestuff layer 2 and an organic transparent top layer 3, an intermediate layer 5 which prevents injection of the charge carriers.

Suitable electroconductive support materials are materials which hitherto have been used for this purpose, for example aluminum foils or transparent plastic sup ports to which aluminum, gold, copper, zinc, cadmium, indium, antimony, bismuth, tin, lead or nickel has been laminated or applied by vapor deposition. Generally, any support may be used which has been made sufficiently electroconductive.

An organic intermediate layer, or also a metal oxide layer produced by a thermal, anodic or chemical process, (such as, e.g., an aluminum oxide layer) may be applied to the electroconductive support. This layer serves the purpose to reduce or prevent the injection of charge carriers from the electroconductive support into the organic dyestuff layer in the absence of light. In addition thereto, it improves the adhesion of the dyestuff layer to the support. Besides the inorganic oxide layers already mentioned, layers of organic materials may also be used. Natural or synthetic resins are suitable which are not or not noticeably dissolved when the top layer is applied, e.g. polyamide resins or polyvinyl phosphonic acid.

An organic intermediate layer may have a thickness of approximately 1 uum, a metal oxide layer may range in thickness from about 10 to 10 Angstrom.

The organic dyestuff layer of the electrophotographic recording material of the invention substantially determines the spectral light-sensitivity of the photoconductive double layer of the invention.

Examples of suitable dyestuffs are listed in the attached table of formulae. In the table, Formula I is phthalocyanine.

Formula 2 is a phthalocyanine compound containing a metal, e.g. copper ll, cadmium, zinc or lead. The compound may be substituted at the phenyl residue by a lower alkyl group, by halogen, or by nitro groups.

Formula 3 represents macrocyclic compounds having a conjugated 'rr-electron system, in which B and B, instead of benzpyrrole groups, are preferably phenylene, naphthylene or pyridylene groups which may be substituted by the above mentioned substituents. in this case, too, compounds with or without a metal content may be used.

Formula 4 represents a porphin system in which R stands for lower alkyl, phenyl, or phenyl substituted by a lower alkyl group or by halogen. The porphin system may also contain a metal such as the ones mentioned above. it was found, however, that it is preferable to use porphin compounds without such metal content and that the metal-containing porphin compounds are only occasionally more advantageous with regard to the preferred vacuum deposition application.

The dyestuffs are known organic compounds which are described, for example, in Colour Index, Second Edition, Vol. 3 (1956). Thus, metal-free phthalocyanine corresponding to Formula 1 (Cl. 74 is marketed under the names of Heliogenblau G" (BASF, Ludwigshafen, Germany), Monastralechtblau GS" or Monolite Fast Blue GS (lCI, London, England) and copper phthalocyanine corresponding to Formula 2 (Cl 74 is available under the designations Chromophthalblau 4 G (Ciba-Geigy, Basle, Switzerland), Heliogenblau B" or "LBGT" (BASF, Ludwigshafen, Germany).

Further suitable dyestuffs are described in Phthalocyanine Compounds by F. H. Moser and A. L. Thomas (Reinhold Publishing Corporation, New York, 1963 They include phthalocyanine compounds which are substituted at the benzpyrrol nucleus by a lower alkyl group or by halogen, as well as tetraaza and octaaza phthalocyanines.

Some of the products are commercially available in the pure form, whereas others must be repeatedly purified before they can be used in electrophotographic layers, by reprecipitation in concentrated sulfuric acid, by extraction, or by digestion in solvents. The application by vapor deposition, which is preferred for the present invention, may also serve as a purifying method.

Conjugated macrocyclic compounds containing two benzpyrrol groups and two further aromatic or heterocyclic groups (Formula 3) are also suitable as dyestuffs to be used according to the invention. Because of their orange-yellow to red color, the range of their highest photosensitivity is displaced to the shorter wave length range (450 to 550 nm). The compounds are described by P. F. Clark, 1. A. Elvidge, and R. P. Linstead in Journal of the Chemical Society, 1954, pages 2490 to 2497.

Other macrocyclic compounds which may be used for the present invention are porphins. These compounds are prepared as described by A. D. Adler et al. in J. Org. Chem., 32, 476. Formula 4 shows, as an example, the meso-tetraphenylporphin in which R stands for phenyl.

when used in multi-layer materials, with the top layers described further down, the phthalocyanines display a very high degree of photosensitivity within the spectral range between 550 and 750 nm. Photoconductor layers containing phthalocyanines are thus particularly suitable for use in reproduction machines equipped with halogen/tungsten lamps as light sources. Further, the phthalocyanine compounds with or without metal content have the advantage that they are readily accessible, can be easily purified, can be vacuum-deposited under favorable conditions, and possess good adhesion to aluminum foils or aluminum-coated polyester films.

X-ray diffraction patterns of the vapor-deposited layers and examinations by infrared spectroscopy show that under the conditions maintained during vacuum deposition (pressure of 5 X mm Hg, temperature of 360 to 390 C), the a-form of the metal-free phthalocyanine is normally formed.

Due to the use of the dyestuffs according to the present invention, a multi-layer material is obtained which is highly light-sensitive, so that the organic photoconductor layer of the invention may be arranged on 2. cylindrical drum or on an endless web for use in an electrophotographic apparatus.

As already mentioned, the dyestuffs according to the invention possess a very high degree of photosensitivity when arranged in these double layers, they can be easily prepared and can be purified without difficulties. Moreover, they possess a good thermal and photochemical resistance, so that they can be applied, e.g. under reduced pressure, without being decomposed and undergo no photochemical alterations under xerographic conditions. in particular, the thin dyestuff layer according to the invention has the following advantages:

l The production of charge carriers at the boundary surface between dyestufflayer and top layer, is particularly high, and

2. the charge transport through the tightly packed dyestuff layer is not impeded by binders.

Moreover, the adhesion between the electroconductive support and the dyestuff layer is very good, so that photoconductor layers of good bond strength are obtained upon application of the top layer.

The organic dyestuff layer must be extremely uniform since only its uniformity guarantees a uniform injection of charge carriers into the top layer. To achieve this object, the dyestuff layers are applied according to special coating methods. Such methods are the application by mechanically rubbing the most finely powdered dyestuff material into the electroconductive support material, the application by chemical deposition of a leucobase to be oxidized, for example, the application by electrolytical or electrochemical processes or the gun spray method. The application preferably is performed, however, by vapor depositing the dyestuff in the vacuum. A tightly packed homogeneous coating is achieved thereby.

The tightly packed coating makes it unnecessary to produce thick dyestuff layers for achieving a high absorption. The tightly packed dyestuff molecules and the extremely low layer thickness permit, in a particularly advantageous manner, the transport of charge carriers so that it is completely sufficient to produce the charge carriers at the boundary layer only.

The application of the dyestuff layer by vapor deposition in the vacuum requires dyestuffs with thermal resistivity in the temperature range to be applied for vapor deposition. The high extinction of the dyestuff allows high concentration of excited dyestuff molecules. Excitation (I) and charge separation (2) take place in the dyestuff layer according to the following reaction equations:

2. 5 S -s -8 with S dyestuff molecule 8* excited dyestuff molecule, and

'5 'S dyestuff radical ions.

At the boundary surface between the organic dyestuff layer and the transparent top layer, reactions of the excited dyestuff molecules or the resulting charge carriers in the form of the dyestuff radical ions with the molecules of the charge transport effecting compound in the top layer are possible according to the following equations:

6. F2 S 'F26 with F, donor molecule F acceptor molecule F F donor or acceptor radical ion.

At the boundary surface, sensitizing reactions take place between the transparent top layer and the organic dyestuff layer. The top layer thus is a sensitized organic photoconductor at least in the area of the boundary surface, which leads to the surprisingly high photoconductivity.

Reactions 3 and 5 proceed preferably when the IT-61Ctl0l1 system in the top layer is a compound which, as a donor compound, easily can release electrons. This is the case with 2,5-bis-(p-diethylaminophenyl)-1,3,4-oxadiazole, for example. Reactions 4 and 6 are preferably possible with a substance in the top layer which, as an electron acceptor, easily accepts electrons, e.g. 2,4,7-trinitrofluorenone or N-t-butyl- 3,o-dinitro-naphthalimide.

Due to the characteristic features of the invention it is sufficient for the efficiency of the dyestuff when, hesides its intense absorption, it only has either electronattracting substituents, e.g. C=0, NO2, halogen,

or electronrepelling substituents, e.g. -NH2, N alkyl or O-alkyl, depending on whether it is preferably suitable for reactions 3,5 or 4,6. The invention permits charge carrier transport fostered by a particularly low expenditure of energy within the tightly packed dyestuff layer according to the following reactions:

8. S+'S -S+ S. 1n all conventional sensitizing processes, however, transport via the dyestuff molecules present in low concentration is impeded by their large distance from one another.

Analogous is the procedure of the charge transport in the top layer with:

9. Fi -t F1 F1+Fi (p-conductive) 10. -F+ F2 F2 F9 (n-conductive) The practical consequence of reactions 1 to 10 is that, in the use of electron donors in the top layer, the double layer arrangement is negatively charged so that reactions 3,5,8,9 can proceed. in the inverse case, layers with electron acceptors in the top layer are positively charged so that reactions 4,6,7, and 10 can proceed.

The transparent top layer of organic insulating materials containing at least one charge transporting compound is described as follows:

The transparent top layer has a high electric resistance and prevents in the dark the flowing off of the electrostatic charge. Upon exposure to light, it transports the charges produced in the organic dyestuff layer.

If it is to be negatively charged, the transparent top layer preferably consists of a mixture of an electron donor compound and a binder. But when the electrophotographic recording material is to be used for positive charging the transparent top layer consists preferably of a mixture of an electron acceptor compound and a binder.

Consequently, in the transparent top layer there are used compounds for charge transport which are known as electron donors or electron acceptors. They are used together with binders or adhesives adapted to the compound for charge transport as regards charge transport, film property, adhesion, and surface characteristics. Furthermore, conventional sensitizers or substances forming charge transfer complexes may be present. Buty they can only be used in so far as the necessary transparency of the top layer is not impaired. Finally, other usual additives such as levelling agents, plasticizers, and adhesives may also be present.

Suitable compounds for charge transport are especially those organic compounds which have an extended 'rr-electron system, e.g. monomer aromatic heterocyclic compounds.

Monomers employed in accordance with the invention are those which have at least one dialkyl amino group or two alkoxy groups. particularly proved have heterocyclic compounds, such as the oxadiazole derivatives, mentioned in German Patent No. 1,058,836. An example thereof is in particular the 2,5-bis-(p-diethylaminophenyl)-oxadiazole-1,3,4. Further suitable monomer electron donor compounds are, for example, triphenyl amine derivatives, benzo-condensed heterocycles, pyrazoline or imidazole derivatives, as well as triazole and oxazole derivatives, as disclosed in German Patent Nos. 1,060,260 and 1,120,875.

Formaldehyde condensates of various aromatic compounds, e.g. the formaldehyde condensate of 3- bromopyrene, may also be used.

Besides these mentioned compounds having predominantly a p-conductive character, it is also possible to use n-conductive compounds. These so-called electron acceptors are known from German Patent No. 1,127,218, for example. Compounds such as 2,4,7- trinitrofluorenone or N-t-butyl-3,6-dinitronaphthalimide have proved particularly suitable.

Suitable binders with regard to flexibility, film properties, and adhesion are natural and synthetic resins. Examples thereof are in particular polyester resins, e. g. those marketed under the names Dynapol" (Dynamit Nobel), Vitel (Goodyear), which are copolyesters of isoand terephthalic acid with glycol. Silicone resins as those known under the names SR of General Electric Comp. or Dow 804 of Dow Corning Corp., U.S.A., and which are three-dimensionally cross-linked phenylmethyl siloxanes or the so-called "reactive" resins, e.g. the so-called DD" lacquers consisting of an equivalent mixture of polyesters or polyethers containing hydroxyl groups and polyfunctional isocyanates, e.g. of the Desmophen" or Desmodur" type marketed by Bayer AG, Leverkusen, Germany, have proved particularly suitable. Furthermore, copolymers of styrene and maleic acid anhydride, e.g. those known under the name Lytron, Monsanto, and polycarbonate resins, e.g. the resins known by the name of Lexan Grade" of General Electric, U.S.A., may be used.

The mixing ratio of charge transporting compound to binder may vary. Relatively certain limits are given, however, by the requirement for maximum photosensitivity, is. for the biggest possible portion of charge transporting compound, and for crystallization to be prevented, ie for the biggest possible portion of binder. A mixing ratio of about 1:1 parts by weight has proved preferable, but mixing ratios from about 3:1 to 1:4 or above, depending on the particular case, are also suitable.

The conventional sensitizers to be used additionally may advantageously foster charge transport. Moreover, they may produce charge carriers in the transparent top layers. Suitable sensitizers are, for example, Rhodamine B extra, Schultz, Farbstofftabellen (dyestuff tables), 1st volume, 7th edition, 1931, No. 864, page 365, Brilliant Green, No. 760, page 314, Crystal Violet, No. 785, page 329, and Cryptocyanine, No. 927, page 397. In the same sense as act the sensitizers may also act added compounds which form charge transfer complexes with the charge transporting compound. Thus, it is possible to achieve another increase of the photosensitivity of the described double layers. The quantity of added sensitizer or of the compound forming the charge transfer complex is so determined that the resulting donor acceptor complex with its charge transfer band still is sufficiently transparent for the organic dyestuff layer below. Optimum concentration is at a molar donor/acceptor ratio of about 10:1 to about :1 and vice versa.

The addition of adhesives as binders to the charge transporting compounds especially to polymer compounds of this type already yields a good photosensitivity. in this case, lowmolecular polyester resin, such as Adhesive 49,000, Du Pont, has proved particularly suitable.

In the described manner, the top layers have the property to render possible a high charge with a small dark discharge. Whereas in all conventional sensitizations an increase of the photosensitivity is connected with an increase of the dark current, the arrangement of the invention can prevent this parallelity. The layers are thus usable in electrophotographic copying devices with low copying speeds and very small lamp energies as well as in those with high copying speeds and correspondingly high lamp energies.

The invention will now be described in more detail by reference to the attached examples.

Application of the Dyestuff Homogeneous dyestuff layers consisting of metal free or metal-containing phthalocyanines according to Formula 1 and Formula 2, respectively, are prepared by vacuum deposition under a reduced pressure of approximately 10 to 10" mm Hg (pump: type A-l, marketed by Pfeiffer, Wetzlar, Germany). The distance between the dyestuff and the 100 pm thick aluminum, to which it is applied, is about 15 cm. The temperature during vacuum-deposition is measured directly on the surface of the dyestuff to be vacuum-deposited, by means of a nickel-chromium thermoelement. In the following table, the other conditions used for vacuumdepositing various dyestuffs are listed:

Monolite Fast Blue GS (Formula l) The vacuum-deposited dyestuff layers have a good covering power and good adhesion to the aluminum foil; the weight of the dyestuff layers in the range from 150 to 300 mg/m.

EXAMPLE 1 For the preparation of photoconductive double layers, the above described dyestuff layers are provided with top layers consisting of one part by weight of 2,5- bis-(4-diethylaminophenyl)-oxadiazole-l,3,4 and one part by weight of a polyester resin, e.g. Dynapol L 206" (a product of Dynamit Nobel AG., Troisdorf, Germany). The top layers are produced by whirlcoating a tetrahydrofurane solution of the above components onto the dyestuff layers and drying the resulting coatings for about 5 to minutes at 120C. Homogeneous, glossy layers are thus produced which have a thickness of about 10pm.

The photosensitivity of the double layers thus produced is determined as follows:

The photoconductive double layer is placed on a slowly rotating disk and passed through a charging apparatus (Adjustment: corona 7.0 kV, grid 1.5 kV) to the exposure station where it is exposed to the light of a xenon lamp (Osram, type XBO 150), a heat absorbing glass (type KG3, a product of Schott & Gen., Mainz, Germany) and a neutral filter of transparency being interposed. The intensity of illumination in the plane of measurement is 750uW/cm The altitude of charge (U and the curve of photoinduced light decay of the photoconductive layer are recorded by an oszillographic device over an electrometer (type 160 CR, a product of Keithley Instruments, USA) and a transparent proble.

Upon determining the height of charge (U and the half time (T of these double layers and of a top layer which had been prepared analogously, but without a dyestuff (zero layer), the following values result:

By means of a Dyntestdevice marketed by ECE, Giessen, Germany, the dark decay (AU of these layers two seconds after reaching their saturation charge is also measured.

EXAMPLE 2 Homogeneous dyestuff layers produced as in Example 1 from a dyestuff corresponding to Formula 1, e.g. Monolite Fast Blue GS" are coated with about lOum thick top layers of the type described in Example 1 which have been activated by different concentrations of an acceptor compound. Composition of the top layers:

a. one part by weight of oxadiazole derivative mentioned in Example 1 and one part by weight of a polyester resin;

b. same components as in (a), plus 0.025 part by weight of 3,5-dinitrobenzoic acid;

c. same components as in (a) plus 0.1 part by weight of 3,5-dinitrobenzoic acid.

After drying, homogeneous, glossy top layers are obtained. it turns out that a higher proportion (0.1 part by weight) of 3,5-dinitrobenzoic acid produced an undesirable crystallization tendency in the top layer,

The photosensitivity and the dark decay of the double layers is determined as described in Example 1, the light-intensity in the plane of measurement being 615uW/cm:

with top layer (c) The double layer comprising top layer (a) was selected to have its spectral light-sensitivity measured, the method applied being as follows: The material is negatively charged and then its half time (T for the different wave length ranges of the spectrum is determined by exposing it to the light of a xenon lamp (type XBO while interposing monochromatic filters (line filters, half time range 10-12 nm, a product of Schott & Gen., Mainz, Germany). By plotting the reciprocal values of the product of half time T m (in sec onds) and lightintensity l W/cm) against the wave length A (nm) the spectral light-sensitivity of the d6ll= ble layer is determined, as shown in FIG. 3. The ffifilptrocal value of T -1 is the light energy, per unit area,

which must be irradiated to discharge the layer to half its original charge U Besides 3,5-dinitro benzoic acid, other acceptor compounds may also be used in the top layers. A vacuum deposited dyestuff layer of purified Heliogenblau G" (Formula l) is coated with solutions of the follow ing compositions:

one part by weight of the oxadiazole derivative used in Example 1,

one part by weight of the polyester resin used in Example l, and

O.l part by weight of an acceptor compound, viz.

a. 2,4,7 trinitro-fluorenone 9 b. 2,6-dinitrobenzoic acid,

c. 3-trifluoro-methyl-benzoic acid, and d. 4-nitropyridine-N-oxide.

The resulting layers have a thickness of approximately lO Lm. The photosensitivity of the double layers is determined as described in Example 1, using a xenon lamp (light-intensity 6l Saw/cm):

Heliogenblau G" corresponding to Formula 1 (a product of BASF, Ludwigshafen, Germany) is vacuum deposited, in its oz-form, on an aluminum foil under the conditions stated in Example 1.

A photoconductive double layer of about 10pm thickness is produced by coating this dyestuff layer with a solution of one part by weight of 2,5-bis-(4-diethylaminophenyl)-oxdiazole'l .3,4, one part by weight of a polyester resin, e.g. Dynapol L 206", and 0.1 part by weight of 3,5-dinitrobenzoic acid.

in order to measure its photosensitivity, the photoconductive double layer produced in this manner is charged to a negative potential by passing it 3 times through a charging apparatus (types AG 56, a product of KALLE AKTIENGESELLSCHAFT, Wiesbaden- Biebrich Germany) adjusted to 7.5 kV. Subsequently, the charged layer is exposed to the light of a xenon lamp. the intensity of illumination in the plane of measurement being approximately 300 lux. Height of charge and the curve of the photo-induced light decay of the photoconductor layer are measured by means of an electrometer through a probe.

The photosensitivity of the double layer is compared with that of a top layer alone (zero layer):

Thus, the dyestuff of Formula 1 as it is commercially available (Heliogenblau G) is unsuitable for being vac- 12 uum deposited to produce the double layers according to the invention. Before use, the commercial product must be submitted to an extraction in order to remove any impurities, additives, and possible side-products of its manufacture.

The commercial product is purified as follows:

a. The dyestuff according to Formula 1, e.g. Heliogenblau G" (BASF) is extracted for 48 hours with a l:l mixture of l,2-dichlorobenzene and methanol in a Soxhlet extraction apparatus.

b. Heliogenblau G is digested for 4 hours in dimethyl formamide (DMF) on a water bath of a temperature of C using a Rotavapor" apparatus (Biichi KG, Zurich, Switzerland).

The purified and dried products are vacuum deposited in the normal manner, and the double layers are produced and measured as described in the preceding examples:

Layer U,,(V) T l/2 M neg. charge (msee) EXAMPLE 4 The influence of sensitizers contained in the top layer of a photoconductive double layer material is demonstrated by means of the following examples. For this purpose, the charge transporting compound of Example l (oxadiazole derivative) is sensitized in the red wave length range of the spectrum by Brilliant Green (C. I. 42, 040), in the yellow-green range by Rhodamine B (Schultz, Farbstofftabellen", Leipzig, I93], Vol. I, No. 864, page 365), and in the blue range by trianisylpyrylium-perchlorate. The homogeneous, glossy dyestuff layers produced from the dyestuffs according to Formula 1 are coated with the following solutions:

a. one part by weight of 2,5-bis-(4-diethylaminophenyl)-oxdiazole-l ,3,4 and one part by weight of a polyester resin, e.g. Dynapol L206" b. as in (a) lO part by weight of Brilliant Green c. as in (a) 10 part by weight of Rhodarnine B d. as in (a) IO part by weight of trianisyl-pyrylium-perchlorate. After drying, the top layers are about 10pm thick.

The photosensitivity of the thus sensitized double layers is measured as described in Example 3 (approx. 300 lux in the plane of measurement; dark decay is determined by Dyntestapparatus):

The dyestufi according to Formula I is applied to anodically oxidized aluminum foils under the conditions described above. The A1 layers have a thickness of approximately 100 and 300 Angstrom, respectively.

The dyestuff layers are then coated with an about I0p.m thick top layer of the following composition:

one part by weight of 2,5'bis-(4-diethylaminophenyl )-oxadiazole- I ,3,4, one part by weight of a polyester resin (e.g. Dynapol L206") and 0.I part by weight of 3,5-dinitrobenzoic acid.

The photosensitivity is measured as described in Example 3 for xenon light, the light intensity being 300 lux in the plane of measurement:

For the preparation of an organic intermediate layer (numeral 5 in FIG.2) a 2 per cent solution of a polyamide resin (e.g. Elvamide 8061, a product of DuPont, USA) in a l:l mixture of trichloroethylene and methanol is applied to a IOOum thick polyester film provided with a vacuum deposited aluminum layer. The intermediate layer thus produced has a thickness of less than Ium; in the present example, the weight of the layer is 0.2 g/m Then a dyestuff layer consisting of metal-free phtha- Iocyanine, e.g. ofMonolite Echt Blau GS", is vacuum deposited on the precoated material as described above, and on top of the dyestuff layer a top layer is produced consisting of one part by weight of the oxadiazole derivative used in Example I and one part by weight ofa polyester resin, e.g. Dynapol L 206. After drying the layer for 5 minutes at 120C, it has a thickness of about 911m.

The photosensitivity of this muIti-Iayer material is measured by the method described in Example 1 (lightintensity 750p.W/cmc in the plane of measurement) and yields the following values:

negative charge: I I75 V half time T 7 msec.

The dark decay (A u) of this layer is measured by means of a Dyntest-90 apparatus marketed by ECE, Giessen, Germany. After 2 seconds, it is 130 V.

EXAMPLE 7 This example shows the photosensitivity as a function of the thickness of the top layer. For this purpose, dyestuff layers containing dyestuffs of Formula I are vacuum deposited on aluminum foils, and the dyestuff layers are then provided with top coatings from a solution of one part by weight of 2,5-bis-(4-diethylaminophenyl )-oxdiazole- 1 ,3,4, one part of weight of a polyester resin (e.g. Dynapol L206) and 0.1 part by weight of 5 3,5-dinitrobenzoic acid in tetrahydrofurane. By varying the adjustment of the centrifuge, top coatings of different thicknesses are produced. The photoconductor layers thus produced are dried during 30 minutes at 105C. By the method described in Example 3 (lightintensity approximately 300 lux, xenon lamp), the photosensitivities of layers having the following thicknesses are determined:

l5 Thickness U,, (V) T 1/2 Dark Decay (11m) neg. charge (msec) A U,

I 2 I05 27 70 approx. 7 940 34 I40 approx. I0 1175 38 I60 approx. 9 75 49 290 EXAMPLE 8 A solution consisting of one part by weight of 2- phenyl-4-(Z-chlorophenyl)-5-(4-diethylaminophenyI)- Negative charge: 540 V half time T 38 msec.

40 For comparison purposes, a zero layer is produced which displays the following values:

Homogeneous, glossy dyestuff layers consisting of metal-free phthalocyanine are whirl-coated with one of the following solutions:

a. one part by weight of the oxadiazole derivative used in Example I, one part by weight of a styrene/maleic anhydride copolymer (e.g. Lytron 820", a product of Monsanto Chemical Comp., USA) in tetrahydrofurane as the solvent, or

b. one part by weight of the oxadiazole derivative used in Example 1, one part by weight of a threedimentionally cross-linked phenyI-methylsiloxane resin (e.g. Silikonharz SR 182" of General Electric Co., USA 60% in toluene) in toluene as the solvent,

c. one part by weight of the oxadiazole derivative used in Example I, 0.4 part by weight ofDesmophen 1 I00" and 06 part by weight of "Desmodur HL" in tetrahydrofurane as the solvent.

After having been dried for 5 to I5 minutes at 120C, the double layers have a thickness of about 9pm.

The following photosensitivities are determined at a light-intensity of 615;.tW/cm in the plane of measurement (xenon lamp):

Layer U (V) T 1/2 Dark Decay neg. charge (msec) A U a 770 32 125 b 410 23 160 c 550 14 120 EXAMPLE [0 Dyestuff layers consisting of metal-free phthalocyanine according to Formula 1 (e.g. of Monolite Echt Blau GS") are produced on 70pm thick aluminum foils at a pressure of 5 X mm Hg in a high vacuum deposition apparatus (type CVE- S of Bendix Vacuum Division, Friedberg, Germany).

The distance between the heated vessel containing the dyestuff and the aluminum support is 16 cm. The temperature during the vacuum deposition process, measured on the surface of the dyestuff by means of a nickel/chromium thermoelement, is between 270 and 310C. The support is mounted on a drum which rotates at a speed of 20 revolutions per minute during vacuum deposition.

By varying the duration of the vacuum deposition process, while maintaining the remainder of the coating conditions, dyestuff layers of different thicknesses are produced. The weight of the dyestuff is determined by weighing the material once with the layer and once after removal of the layer.

The dyestuff layers produced in this manner are then coated with a solution containing one part by weight of the oxadiazole derivative used in Example 1, and one part by weight of a polyester resin, e.g. Dynapol L206, dissolved in tetrahydrofurane as the solvent.

After having been dried for 5 minutes at 120C, the top layers have a thickness of about 9pm.

For comparison, a zero layer (without a dyestuff layer) is also produced.

The photosensitivities of the layers is determined as described in Example 1, with a xenon lamp and an intensity of illumination of approximately 6l5uW/cm:

The dark decay is measured by means of a Dyntest-90 device of ECE, Giessen, Germany, as described in Example 1.

EXAMPLE 11 A solution containing 81.4% of polyvinyl carbazole (e.g. Luvican M 170", a product of BASF, Ludwigshafen, Germany) and 18.6% of an adhesive polyester resin (e.g. Adhesive 49000", a product of DuPont, USA) in tetrahydrofurane as the solvent is whirl-coated onto a dyestuff layer according to Formula 1 disposed on a 100;.tm thick aluminum foil. After drying, the resulting layer has a thickness about 5 to 6 pm. The homogeneous, flexible double layers thus produced possess a considerably higher photosensitivity than polyvinyl carbazole layers containing no dyestuff layer. The measurements are made at a light-intensity of 61 5 LW/cm Layer according to the invention:

Negative charge: 650 V Half time (T 385 msec.

Zero Layer:

Negative charge: 550 V Half time (T 1000 msec.

EXAMPLE 12 3-bromopyrene resin (prepared by condensing bromo-pyrene Org. Synth., Vol. 48, 1968, Page 30 with formaldehyde in glacial acetic acid) is used as the polymer charge transporting material in the top lay ers according to the invention, by applying one part by weight thereof together with two parts by weight of a polyester resin (e.g. Dynapol L206) in a tetrahydrofurane solution to a dyestuff layer containing a dyestuff according to Formula 1, e.g. Monolite Echt Blau GS". After drying, the top layer has a thickness of approximately 10pm. The photosensitivity is measured as described in Example 1 (light intensity 615uW/cm).

Layer according to the invention:

Negative charge: 485 V Half time (T 240 msec.

Zero Layer:

Negative charge: 650 V Half time (T 465 msec.

EXAMPLE l3 Dyestuff layers containing metal-free phthalocyanine, e.g. Heliogenblau G" purified as described in Example 3, and disposed on an aluminum support are whirl-coated with about 10pm thick top layers produced from solutions containing polyvinyl carbazole (PVCa) (e.g. Luvican M 170") and 2,4,7- trinitrofluorenone (TNF) in varying molar ratios. Fur ther the layer contains about 10 per cent, based on the solids contant, of an adhesive polyester component, e.g. Adhesive 49000".

After drying for 5 minutes at C, homogeneous, flexible photoconductor layers are obtained.

The photosensitivity of the double layers is compared with that of a zero layer (containing no dyestuff) of the same thickness.

The measuring conditions correspond to those in Example 1, e.g. xenon lamp and intensity of illumination of approximately 615;.tW/cm. The results are listed in the following table:

By the method described by P. F. Clark et al. in .1. Chem. Soc." (1954), pages 2490-2497, a crossconjugated, l6-membered annular compound of the attached formula 3 in which 8,8 is m-phenylene, is

produced by condensing l,3-diimino-isoindoline with m-phenylene diamine. After recrystallization from nitro-benzene. bright yellow crystals are obtained which melt at 380C. Under the conditions stated in earlier examples, the compound may be vacuum deposited during 3 to 5 minutes at 250 to 300C to form a homogeneous yellow dyestuff layer. Onto this dyestuff layer, a solution of one part by eight of 2,5-bis-(4- diethylaminophenyl)oxadiazole-l,3,4, one part by weight of a polyester resin, e.g. Dynapol L206, and (ll part by weight of 3,5-dinitrobenzoic acid is whirlcoated in such a manner that the dry top layer has a thickness of approximately pm.

The photosensitivity and the dark decay of the resulting double layer are determined as in Example 1 (light intensity in the plane of measurement 6l5uW/cm Negative charge: 1025 V Half time (T112) 80 msec. Dark Decay after 2 seconds: 0.

EXAMPLE A dyestuff layer consisting of meso-tetraphenylporphin (Formula 4, with R phenyl) is vacuum deposited on a polyamide intermediate layer prepared as described in Example 6. Vacuum deposition occurs within 2 minutes at 330C.

The meso-tetraphenyl-porphin dyestuff is prepared by heating pyrrol and benzaldehyde for a short time in propionic acid according to the method described in J. Org. Chem., 32, page 476.

Layer U (V) T l/Z (neg. charge) (msec) Double layer l000 V. 320

zero layer -l020 V. 370

it will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

l. Electrophotographic recording material comprising an electroconductive support and a photoconductive double layer of organic materials thereon, said double layer being composed of a homogeneous, opaque, charge carrier producing dyestuff layer of a dyestuff corresponding to the general formula A B A N Z l A B A wherein Z is hydrogen or two groups Z together stand for a bivalent metal atom,

A is nitrogen or CR, with R being hydrogen, alkyl with l to 4 carbon atoms, phenyl, which may be substituted by alkyl with l to 4 carbon atoms or halogen, and

B is an m-phenylene, 2,6-pyridylene,

isoindolylene or pyrrolylene group, and

D is hydrogen, or two groups D together stand for a group I? or /N c N i H with the proviso that I. if B is m-phenylene or 2,6-pyridylene, A is nitrogen and two groups D together stand for a group I'll or /ND C N 2. if B is l,3-isoindolylene, A is nitrogen and two groups D together stand for a group and 3. if B is pyrrolylene, A is CR and D is hydrogen, and

a transparent top layer of insulating materials containing at least one charge transporting compound, in which the transparent top layer is composed of a mixture of a binder with a charge-transporting, monomeric heterocyclic compound having an extended 1r-electron system which is substituted by at least one dialkylamino group or by two alkoxy groups, or with a condensation product of 3- bromopyrene and formaldehyde.

2. Electrophotographic material according to claim 1 in which the heterocyclic compound is selected from the group consisting of oxazoles, oxadiazoles triazoles, imidazoles and pyrazoles.

3. Electrophotographic material according to claim 1, in which the heterocyclic compound is an oxadiazole.

4. Electrophotographic material according to claim 1, in which the heterocyclic compound is 2,5-bis-(4- diethyl-aminophenyl)-oxadiazolel ,3,4.

5. Electrophotographic material according to claim 1, in which the heterocyclic compound is an oxazole.

6. Electrophotographic material according to claim 1, in which the heterocyclic compound is 2-phenyl-4- (2chlor0phenyl)-5-(4-diethylaminophenyl)-oxazole.

7. Electrophotographic material according to claim 1, in which the dyestuff layer has a thickness from about 0.005 to about 2pm and the transparent top layer has a thickness from about 5 to about am.

8. Electrophotographic material according to claim 1, in which the transparent top layer consists of a l:l mixture of the chargetransporting compound and the binder.

9. Electrophotographic material according to claim l, in which the binder is selected from the group consisting of polyesters or copolyesters, silicone resins, reactive resins of polyethers or polyesters and polyfunctional isocyanates, styrene/maleic anhydride copolymers, and polycarbonate resins.

l0. Electrophotographic material according to claim layer.

t i l i 

1. ELECTROPHOTOGRAPIC RECORDING MATERIAL COMPRISING AN ELECTROCONDUCTIVE SUPPORT AND A PHOTOCONDUCTIVE DOUBLE LAYER OF ORGANIC MATERIAL THEREON. SAID DOUBLE LAYER BEING COMPOSED OF A HOMOGENEOUS OPAQUE, CHARGE CARREN PRODUCING DYESTUFF LAYER OF A DYESTUFF CORRESPONDING TO THE GENERAL FORMULA
 1. IF B IS M-PHENYLENE OR 2,6-PYRIDYLENE, A IS NITROGEN AND TWO GROUPS D TOGETHER STAND FOR A GROUP
 2. IF B IS 1,3-ISONINODOYLENE, A IS NITROGEN AND TWO GROUPS D TOGETHER STAND FOR A GROUP
 2. if B is 1,3-isoindolylene, A is nitrogen and two groups D together stand for a group
 2. Electrophotographic material according to claim 1 in which the heterocyclic compound is selected from the group consisting of oxazoles, oxadiazoles, triazoles, imidazoles and pyrazoles.
 3. Electrophotographic material according to claim 1, in which the heterocyclic compound is an oxadiazole.
 3. if B is pyrrolylene, A is CR and D is hydrogen, and a transparent top layer of insulating materials containing at least one charge transporting compound, in which the transparent top layer is composed of a mixture of a binder with a charge-transporting, monomeric heterocyclic compound having an extended pi -electron system which is substituted by at least one dialkylamino group or by two alkoxy groups, or with a condensation product of 3-bromopyrene and formaldehyde.
 3. IF B IS PYRROLYLENE, A IS CR AND D IS HYDROGEN, AND A TRANSPARANT TOP LAYER OF INSULTING MATERIALS CONTAINING AT LEAST ONE CHARGE TRANSPORTING COMPOUND, IN WHICH THE TRANSPARENT TOP LAYER IS COMPOSED OF A MIXTURE OFA BINDER WITH A CHARGE-TRANSPOTING, MONOMERIC HETEROCYCLIC COMPOUND HAVING AN EXTENDED -$-EECTRON SYSTEM WHICH IS SUBSTITUDED BY AT LEAST ONE DIALKYLAMINO GROUP OR BY TWO ALKOXY GROUPS, OR WITH A CONDENSATION PRODUCT OF 3BROMOPYLENE COMPOSITION FROM AN ORGANIC POLYMERIC PHOTOCO
 4. Electrophotographic material according to claim 1, in which the heterocyclic compound is 2,5-bis-(4-diethyl-aminophenyl)-oxadiazole-1,3,4.
 5. Electrophotographic material according to claim 1, in which the heterocyclic compound is an oxazole.
 6. Electrophotographic material according to claim 1, in which the heterocyclic compound is 2-phenyl-4-(2-chlorophenyl)-5-(4-diethylaminophenyl)-oxazole.
 7. Electrophotographic material according to claim 1, in which the dyestuff layer has a thickness from about 0.005 to about 2 Mu m and the transparent top layer has a thickness from about 5 to about 20 Mu m.
 8. Electrophotographic material according to claim 1, in which the transparent top layer consists of a 1:1 mixture of the chargetransporting compound and the binder.
 9. Electrophotographic material according to claim 1, in which the binder is selected from the group consisting of polyesters or copolyesters, silicone resins, reactive resins of polyethers or polyesters and polyfunctional isocyanates, styrene/maleic anhydride copolymers, and polycarbonate resins.
 10. ElectrophotOgraphic material according to claim 1, in which the binder is a copolymer of isophthalic acid and/or terephthalic acid and glycol.
 11. Electrophotographic material according to claim 1, in which the binder is a styrene/maleic anhydride copolymer.
 12. Electrophotographic material according to claim 1, in which the binder is a low molecular weigght polyester resin.
 13. Electrophotographic material according to claim 1, in which the transparent top layer additionally contains sensitizers and/or substances forming charge-transfer complexes.
 14. Electrophotographic material according to claim 1, in which an insulating intermediate layer is disposed between the support and the photoconductive double layer. 